1. Field of the Invention
The present invention relates generally to the field of submergible pumping systems for raising fluids from wells, such as petroleum production wells. More particularly, the invention relates to a novel shroud arrangement that permits fluids to be channeled between components of a submergible pumping system and that compensates for thermal expansion of system components during operation.
2. Description of the Related Art
Various types of pumping systems are known for raising fluids from wells, such as petroleum production wells. Such wells generally include a wellbore extending through subterranean formations and a casing defining the inner periphery of the wellbore. The casing is perforated in the vicinity of one or more production zones. Such production zones typically comprise subterranean geological formations bearing minerals of interest, such as crude oil, waxes, gas, and so forth. The fluids flow into the wellbore through the perforations and collect in the wellbore. Where pressure within the well is insufficient to raise the fluids to the earth's surface by natural means, artificial means are employed to exploit the well.
One well known technique for raising fluids from wellbores involves submerging a pumping system in the wellbore fluids and driving the pumping system to force fluids to the earth's surface. Such pumping systems typically include an electric motor coupled to a production pump. The electric motor and production pump are submerged in the wellbore fluids and the electric motor is coupled to a power supply and control cable extending from circuitry above the earth's surface. When the pump is driven in rotation, wellbore fluids are drawn into the pump and forced through a conduit, such as coil tubing, to a collection point above the earth's surface.
Such pumping systems may also include equipment designed to handle nonproduction fluids. In many wells, fluids entering the wellbore include both production fluids of commercial interest, as well as non-production fluids, such as water, brine and so forth. While non-production fluids can also be raised to the earth's surface and separated from the fluids of interest, it is often more economical to separate the fluids within the wellbore and to raise only the production fluids to the earth's surface. Accordingly, various types of separators may be included in the pumping system for separating the production and non-production fluids in situ. The non-production fluids can be reinjected into a discharge or injection zone of the well directly from the separator, or may be injected into such a zone by a separate injection pump. The injection pump may be driven by the same electric motor used to drive the production pump, or may be driven by a separate electric motor included in the pumping system.
In submergible pumping systems of the type described above, it is often necessary to convey fluids from one of the system components to another. For example, in systems including a fluid separator, production fluids are commonly routed from the separator to the inlet of the production pump. In many cases, it is preferable to route such fluids around the electric motor to assist in convectively cooling the motor during operation. Shrouds have been developed to facilitate routing of such fluids in pumping systems. In general, such shrouds constitute an annular conduit disposed about a portion of the pumping system, leaving a space between the system components and the shroud wall. Fluids flow within the annular space between the system components, preferably passing along the outer wall of the submergible electric motor. Shrouds of this type not only facilitate cooling of the electric motor, but in many cases simplify piping within the pumping system, eliminating the need for separate conduits between the system components. Moreover, such shrouds often maximize the cross sectional area available for the flow of fluids between the system components, as compared to pipes, tubes or other conduits which may be connected and extend adjacent to the pumping system within the wellbore.
Shrouds currently used in submergible pumping systems suffer from several important drawbacks. Most notably, conventional shrouds do not offer adequate compensation for thermal expansion and contraction of the system components. In particular, the motors, pumps, separators, and ancillary components of submergible pumping systems may extend over substantial lengths within the well. In addition, the system components may be subjected to a wide range of temperatures. For example, ambient temperatures at the location where the system is built and temperatures outside the well location may vary considerably. Moreover, temperatures within the wellbore may rise substantially (e.g., 200.degree. F. or more) during periods of operation of the system, fluctuating both due to natural changes in the fluid temperatures, as well as due to heat generated by operation of the pumping system.
Under such conditions, the pumping system components and shrouds experience changes in length owing to their respective coefficients of thermal expansion. Such thermal expansion can impose significant stresses on the system components and shrouds, particularly where the rates of thermal expansion of the components and the shrouds are not the same, or where the components and the shrouds experience different temperatures, as may be the case in certain applications. Such stresses can result in weakening of the system components or the shrouds, or in leakage about the points of connection between the pumping system and the shroud.
There is a need, therefore, for an improved technique for directing fluids between components of submergible pumping systems. In particular, there is a need for a shroud configuration which automatically adjusts or compensates for variations in length of pumping system components, such as may result from thermal expansion.